A talk by Roger Avery on Monday 16th September 2019 at Spurgeon Hall,
Roger worked as a Senior Lecturer in Zoology at Bristol University, before retiring and moving to Devon many years ago. For his PhD he studied tapeworms in birds at Slimbridge Wildfowl Trust, working mainly on ducks and geese, where he met Sir Peter Scott and gained an insight into many aspects of bird colouration. Twenty nine members were present to hear a very interesting and wide ranging talk about the types and reasons for bird colouration and patterning, with several amusing anecdotes.
Birds use instinct for many behavioural traits and visual signals are an important factor, hence the need for striking colours. Roger described David Lack’s work on Robin behaviour, where he showed that the red breast was the key signal for defending territories. A Robin without a red breast was ignored if it entered another Robins’ territory, while a bunch of red feathers could sometimes be attacked.
Colour and patterns are also employed by birds for recognition. In Bewick Swans the yellow bill markings are distinct for each individual bird. As they migrate in family groups, the ability to recognise family members is important, especially for the juveniles.
The red mark on the lower mandible of the beak of Herring Gulls is a colour signal for the chicks to peck here, causing the adults to regurgitate food for them. It is not a mark left by ketchup after adult birds have eaten chips – as Roger overheard one mother telling her child. Research by Tinbergen showed that the chicks only peck ‘red spots of the correct size’. He found that it does not matter where on the body the spot is placed, the chicks will still see it as a signal to peck for food.
Camouflage is the main reason for the colours and patterns seen on many birds, such as the Bittern. It hides in reed beds and closely mimicks the background of upright reeds.
Colour is also important when choosing a mate. The black band on the breast and underside of Great Tits is a signal of how well fed the bird was as a fledgling. A female will choose a mate with a wide band as this signals that he was well fed in the nest and is more likely to be a healthy, athletic mate.
The reason for the bright colouration of some birds remains a mystery. Why are Kingfishers so brightly coloured? As most birds can also see in the ultraviolet light range, the answers may be more complicated than we think.
After his talk, Roger answered many questions showing his broad spectrum of zoological knowledge. A discussion on bird migration also took place, but as Roger said, this may have to wait for a later talk.